This invention pertains to a pressure-sensitive adhesive and more particularly to a pressure-sensitive adhesive containing a poly(alkylene oxide) copolymer that provides bond formation useful for adhesion to wet surfaces, such as skin or like delicate surfaces.
Pressure-sensitive adhesive (PSA) articles are used in a wide variety of applications where there is a need to adhere to skin, for example, medical tapes, wound or surgical dressings, athletic tapes, surgical drapes, or tapes or tabs used in adhering medical devices such as sensors, electrodes, ostomy appliances, or the like. A concern with many of these adhesive articles is the need to balance the objective of providing sufficiently high levels of adhesion to wet skin as well as to dry skin. Thus, pressure-sensitive adhesives that adhere to wet or moist surfaces, particularly skin, are referred to as xe2x80x9cwet-stickxe2x80x9d adhesives.
One approach in the art to providing pressure-sensitive adhesive articles for application to wet skin has been the use of pattern coated adhesives. A discontinuous adhesive coating on a backing allows the skin to breathe, at least in the areas of the backing not coated with adhesive. This approach is disclosed in U.S. Pat. No. 4,595,001 (Potter, et al.) and U.S. Pat. No. 5,613,942 (Lucast, et al.), as well as EP 353972 (Takemoto, et al.) and EP 91800 (Potter, et al.). These patent documents generally teach intermittent coating of adhesives onto different backings.
(Meth)acrylate pressure-sensitive adhesives are attractive materials for many applications. (Meth)acrylates are known for their optical clarity, oxidative resistance, and inherently tacky nature. Inherently tacky (meth)acrylate pressure-sensitive adhesives (i.e., materials that require no additives such as tackifying resins) are typically formulated predominately from acrylic acid ester monomers of nontertiary alcohols. Examples of such monomers include n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, isononyl acrylate, isodecyl acrylate and dodecyl acrylate. When these (meth)acrylate monomers are polymerized, the homopolymers have a glass transition temperature (Tg) of less than about 10xc2x0 C. This low Tg is a necessary property in (meth)acrylate materials that exhibit tack at room temperature. Such (meth)acrylate polymers are hydrophobic in nature and, without modification, are generally unsuitable as wet-stick adhesives.
A means to increase the hydrophilic character of (meth)acrylate polymers is to copolymerize the (meth)acrylate monomers with hydrophilic acidic comonomers, such as acrylic acid, methacrylic acid, beta-carboxyethyi acrylate, itaconic acid, sulfoethyl acrylate, and the like. Addition of these hydrophilic acidic comonomers in minor amounts (e.g., about 1 weight percent to about 15 weight percent) can also enhance the internal or cohesive strength of the PSA. This increased polymer reinforcement, however, can diminish the tack of the hydrophilic acidic comonomer-containing (meth)acrylate copolymer.
At higher acidic comonomer levels, (meth)acrylate copolymers can dramatically lose their tack and become highly hydrophilic. When exposed to water, the moisture helps to transform these highly acidic, low tack compositions into tacky materials that are suitable as wet-stick adhesives used in many medical applications. When the water is allowed to evaporate, however, these adhesives lose their pressure-sensitive tack. Thus, although this provides suitable wet-stick adhesion in some applications, there is still a need for articles having good initial wet-stick adhesion in other applications, preferably, on the order of the same article""s initial dry-stick adhesion.
Briefly, in one aspect of the present invention, a wet-stick pressure-sensitive adhesive is provided wherein the pressure-sensitive adhesive comprises:
(a) at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester monomer, wherein the (meth)acrylic acid ester monomer when homopolymerized has a Tg of less than about 10xc2x0 C.;
(b) at least one copolymerized hydrophilic acidic monomer; and
(c) at least one nonreactive poly(alkylene oxide) copolymer comprising at least two copolymerized alkylene oxides, at least one of which is hydrophilic (e.g., ethylene oxide) and at least one of which is hydrophobic (e.g., propylene oxide).
In another embodiment is an article that includes a backing and a wet-stick pressure-sensitive adhesive as described above. The adhesives of the present invention adhere to wet surfaces, preferably and advantageously, to wet skin. The glass transition temperature of the adhesive is preferably at least about 10xc2x0 C. The glass transition temperatures of the homopolymers and adhesive are typically accurate to within xc2x15xc2x0 C. and are measured by differential scanning calorimetry.
Yet another embodiment is a method of making a wet-stick pressure-sensitive adhesive. The method includes combining under conditions effective to cause polymerization: at least one monoethylenically unsaturated (meth)acrylic acid ester monomer, which when homopolymerized, has a Tg of less than about 10xc2x0 C.; at least one hydrophilic acidic monomer; and at least one nonreactive poly(alkylene oxide) copolymer comprising at least two copolymerized alkylene oxides, at least one of which is hydrophilic and at least one of which is hydrophobic.
A method of using an adhesive article is also provided. The method involves: providing an adhesive article comprising a backing and a wet-stick pressure-sensitive adhesive layer disposed thereon, wherein the wet-stick pressure-sensitive adhesive comprises: at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester monomer, wherein the (meth)acrylic acid ester monomer when homopolymerized has a Tg of less than about 10xc2x0 C.; at least one copolymerized hydrophilic acidic monomer; and at least one nonreactive poly(alkylene oxide) copolymer comprising at least two copolymerized alkylene oxides, at least one of which is hydrophilic and at least one of which is hydrophobic; and adhering the adhesive article to skin.
As used herein in this application:
xe2x80x9cpressure-sensitive adhesivexe2x80x9d or xe2x80x9cPSAxe2x80x9d refers to a viscoelastic material that displays aggressive tackiness and adheres well to a wide variety of substrates after applying only light pressure (e.g., finger pressure). An acceptable quantitative description of a pressure-sensitive adhesive is given by the Dahlquist criterion, which indicates that materials having a storage modulus (G"") of less than about 4.0xc3x97105 Pascals (measured at room temperature) have pressure sensitive adhesive properties;
xe2x80x9cwet-stick adhesivexe2x80x9d refers to a material that exhibits pressure-sensitive adhesive properties when adhered to at least a wet surface, preferably, to both wet and dry surfaces, particularly skin;
xe2x80x9c(meth)acrylate monomersxe2x80x9d are acrylic acid esters or methacrylic acid esters of nontertiary alcohols, the alcohols preferably having about 4 to 14 carbon atoms;
xe2x80x9chydrophilic acidic monomersxe2x80x9d are water soluble ethylenically unsaturated, free radically reactive monomers having carboxylic acid, sulfonic acid, or phosphonic acid functionality and are copolymerizable with the (meth)acrylate monomers;
xe2x80x9chydrophilic alkylene oxidesxe2x80x9d are monomers that are polymerizable to oligomers or homopolymers that are soluble in room-temperature (25xc2x0 C.) water at 10% by weight;
xe2x80x9chydrophobic alkylene oxidesxe2x80x9d are monomers that are polymerizable to oligomers or homopolymers that are insoluble in room-temperature water at 10% by weight;
xe2x80x9ccopolymerxe2x80x9d includes a polymer of any length (including oligomers) of two or more types of polymerizable monomers, and therefore includes terpolymers, tetrapolymers, etc., which can include random copolymers, block copolymers, or alternating copolymers; and
xe2x80x9cnonreactivexe2x80x9d refers to components that do not contain free radically reactive ethylenically unsaturated groups that could co-react with the comonomers or functionalities or significantly inhibit the polymerization of these monomers.
Generally, the wet-stick pressure-sensitive adhesive of the present invention includes a copolymer that includes at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester monomer, wherein the (meth)acrylic acid ester monomer, when homopolymerized, has a Tg of less than about 10xc2x0 C., and at least one copolymerized hydrophilic acidic monomer. Mixed with this copolymer is at least one nonreactive copolymer comprising at least two copolymerized alkylene oxide monomers, at least one of which is hydrophilic and at least one of which is hydrophobic. Preferably, the pressure-sensitive adhesive adheres to wet skin.
Nonreactive poly(alkylene oxide)s have been used in wet-stick pressure-sensitive adhesives in the past. For example, U.S. Pat. No. 5,733,570 (Chen et al.) teach the use of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) oligomers or polymers. However, PPO is hydrophobic and it is not suitable for the present application as is demonstrated in Comparative Example 2. PEO at low molecular weight (less than about 1000) migrates out of the adhesive formulations because of its low molecular weight and high water solubility. PEO polymers at high molecular weight (greater than about 1000, especially at the preferred range of about 3000-12000) are crystalline materials and will phase separate from the present adhesive compositions.
The ratio of each comonomer in the wet-stick adhesive composition can be chosen to optimize the performance. For example, higher levels of the acidic comonomer can increase the overall Tg and the stiffness of the wet-stick adhesive composition. However, the increased Tg (and modulus) may necessitate higher levels of the poly(alkylene oxide) copolymer. Dependant on the desired end use, higher or lower levels of poly(alkylene oxide) copolymer may be beneficial. For example, if high cohesive strength is desired, typically lower levels of poly(alkylene oxide) copolymer are used.
The present invention also provides articles that include a backing substrate having a continuous or discontinuous adhesive layer disposed thereon. Preferably, such articles have an initial wet skin adhesion of at least about 20 g/2.5 cm (0.8 Newtons/decimeter (N/dm)), and more preferably, at least about 40 g/2.5 cm (1.6 N/dm). Preferably, the initial dry skin adhesion is at least about 20 g/2.5 cm (0.8 N/dm), and more preferably, at least about 40 g/2.5 cm (1.6 N/dm). Preferably, the adhesive article (i.e., a substrate with a continuous or discontinuous layer of adhesive disposed thereon) has an initial wet skin adhesion that is at least about 65%, more preferably, at least about 75%, and most preferably, at least about 100%, of the initial dry skin adhesion. The comparison of wet to dry skin adhesion can be carried out using the test protocol described in the Examples Section. Herein, wet skin has visually observable water thereon.
Inherent viscosity (IV) is a measurement of molecular weight. A higher IV indicates a higher molecular weight. IV and therefore molecular weight can be adjusted by using chain transfer agents such as are known in the art. The preferable IV range for the present application is about 0.3 to about 1.2, and more preferably about 0.5 to about 1.0.
(Meth)acrylate Monomers
The wet-stick adhesives of the present invention contain at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester (i.e., an alkyl acrylate or alkyl methacrylate), wherein the alkyl group has at least about 4 carbon atoms (on average). Alternatively stated, these (meth)acrylate monomers are (meth)acrylic acid esters of nontertiary alkyl alcohols, the alkyl groups of which preferably include about 4 to about 14, more preferably about 4 to about 8, carbon atoms (on average). The alkyl group can optionally contain heteroatoms and can be linear or branched. When homopolymerized, these monomers yield inherently tacky polymers with glass transition temperatures which are typically below about 10xc2x0 C. Preferred (meth)acrylate monomers have the following general Formula (I): 
wherein R1 is H or CH3, the latter corresponding to where the (meth)acrylate monomer is a methacrylate monomer, and R2 is broadly selected from linear or branched hydrocarbon groups and optionally includes one or more heteroatoms. The number of carbon atoms in the hydrocarbon group is preferably about 4 to about 14, and more preferably about 4 to about 8.
Examples of suitable (meth)acrylate monomers useful in the present invention include, but are not limited to, n-butyl acrylate, decyl acrylate, 2-ethylhexyl acrylate, hexyl acrylate, isoamyl acrylate, isodecyl acrylate, isononyl acrylate, isooctyl acrylate, lauryl acrylate, 2-methylbutyl acrylate, 4-methyl-2-pentyl acrylate, ethoxy ethoxyethyl acrylate, and the like. Various combinations of these monomers can be used if desired. Particularly preferred are n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, lauryl acrylate, and mixtures thereof.
Preferably, the copolymerizable mixture of the present invention includes, based upon the total weight of the copolymerizable monomers, at least about 30 weight percent (wt-%), more preferably, at least about 40 wt-%, and most preferably, at least about 50 wt-%, of the (meth)acrylate monomer. Preferably, the copolymerizable mixture of the present invention includes, based upon the total weight of the copolymerizable monomers, no greater than about 80 wt-%, more preferably, no greater than about 75 wt-%, and most preferably, no greater than about 70 wt-%, of the (meth)acrylate monomer.
Hydrophilic Acidic Monomers
Useful copolymerized hydrophilic acidic monomers include, but are not limited to, those selected from ethylenically unsaturated carboxylic acids, ethylenically unsaturated sulfonic acids, ethylenically unsaturated phosphonic acids, and mixtures thereof. Examples of such compounds include, but are not limited to, acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, xcex2-carboxyethyl acrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, vinyl phosphonic acid, and the like. Various combinations of these monomers can be used if desired. Due to their availability and effectiveness in reinforcing (meth)acrylate pressure-sensitive adhesives, particularly preferred hydrophilic acidic monomers are the ethylenically unsaturated carboxylic acids, most preferably acrylic acid.
Preferably, the copolymerizable mixture of the present invention includes, based upon the total weight of the copolymerizable monomers, at least about 5 wt-%, more preferably, at least about 10 wt-%, and most preferably, at least about 15 wt-% of the hydrophilic acid (meth)acrylate monomer. Preferably, the copolymerizable mixture of the present invention includes, based upon the total weight of the copolymerizable monomers, no greater than about 35 wt-%, more preferably, no greater than about 30 wt-%, and most preferably, no greater than about 28 wt-%, of the hydrophilic acid monomer.
Optional Monomers
Minor amounts of monomers copolymerizable with the (meth)acrylate monomers and hydrophilic acidic monomers, such as (meth)acrylamides, vinyl esters, and N-vinyl lactams, can be used. Examples include, but are not limited to, N-alkylated (meth)acrylamides, such as, N-methyl acrylamide, N-ethyl acrylamide, N-methylol acrylamide, N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide, N,N-diethyl acrylamide, N,N-diethyl methacrylamide, N-isopropyl acrylamide, t-butyl acrylamide, N-octyl acrylamide, 4-(N,N-dimethylamido) butylacrylate; N-vinyl lactams, such as, N-vinyl pyrrolidone, N-vinyl caprolactam; and N-vinyl formamide. Various combinations of these monomers can be used if desired. Typically, no more than about 5 wt-% of the total weight of the copolymerizable monomers are used such that the performance of the adhesive is not impaired.
Nonreactive Poly(alkylene oxide) Copolymers
One or more poly(alkylene oxide) copolymers can be combined with the reactive monomers (e.g., (meth)acrylate monomers and hydrophilic acidic monomers) or with the copolymer formed from the reactive monomers. The poly(alkylene oxide) copolymers are selected for use in the wet-stick adhesive such that they improve the pressure-sensitive adhesive characteristics of the copolymerized monomers, are compatible with the copolymerized monomers, and are nonvolatile. Generally, any significant bleeding or migration of the poly(alkylene oxide) copolymer from the adhesive composition is not desirable and could result in loss of wet-stick adhesion properties.
As used herein, a compatible component is one that does not interfere with the polymerization of the monomers and does not phase separate from the wet-stick adhesive composition. By xe2x80x9cphase separationxe2x80x9d or xe2x80x9cphase separate,xe2x80x9d it is meant that visible crystallization or liquid regions do not appear in the adhesive solution or bulk adhesive. Some migration of the poly(alkylene oxide) copolymer from or throughout the wet-stick adhesive composition can be tolerated, such as minor separation due to composition equilibrium or temperature influences, but the poly(alkylene oxide) copolymer does not migrate to the extent of phase separation between the copolymerized acrylate monomers and the poly(alkylene oxide) copolymer.
As used herein, a nonvolatile component remains present and stable under polymerization reaction conditions. Also, to maintain adhesion properties, the poly(alkylene oxide) copolymer remains present and does not significantly evaporate from the adhesive composition. xe2x80x9cNonvolatile componentxe2x80x9d refers to components that, when present in the wet-stick adhesive composition of this invention, generate less than about 3 weight percent VOC (volatile organic content). The VOC can be determined analogously to ASTM D 5403-93 by exposing the coated composition to 100xc2x0 C.xc2x15xc2x0 C. in a forced draft oven for 1 hour. If less than about 3 weight percent of any one component is lost from the pressure-sensitive adhesive composition, then the component is considered xe2x80x9cnonvolatile.xe2x80x9d
Additionally, the poly(alkylene oxide) copolymer is nonreactive to prevent reaction or interference with the polymerization of the copolymer formed from the (meth)acrylate monomers and hydrophilic acidic monomers. However, if the poly(alkylene oxide) copolymer is added during polymerization of the reactive monomers, there could be a small amount (typically, less than about 1 wt-%) that bonds to the pressure sensitive adhesive due to chain transfer. Because this is not a significant amount, the poly(alkylene oxide) copolymer is considered xe2x80x9cnonreactive.xe2x80x9d
The poly(alkylene oxide) copolymers include at least two copolymerized alkylene oxide monomers, at least one of which is hydrophilic and at least one of which is hydrophobic. A preferred copolymer is formed from ethylene oxide and propylene oxide. They can be random, alternating, or block. Preferably, they are block copolymers that include hydrophobic and hydrophilic segments.
Hydrophilic poly(alkylene oxides) typically have higher melting points than hydrophobic poly(alkylene oxides). Thus, the amount of each used to prepare any poly(alkylene oxide) copolymer is balanced to provide the desired melting point of the copolymer. For preferred embodiments of the present invention, the melting point of the poly(alkylene oxide) copolymer is no greater than about 50xc2x0 C. More preferably, the melting point of the copolymer is no greater than about 25xc2x0 C. Such preferred low-melting embodiments are less likely to phase separate from the pressure-sensitive adhesive composition.
Particularly useful poly(alkylene oxide) copolymers have a weight average molecular weight of about 1000 to about 15,000, preferably of about 3000 to about 12,000.
Preferred poly(alkylene oxide) copolymers have appreciable water solubility, preferably, at least about 10 parts per 100 parts of water, exhibit surfactant characteristics preferably having an HLB (hydrophilic lipophilic balance) value of about 3 to about 15, and more preferably, about 5 to about 12. Useful poly(alkylene oxide) copolymers have ratios of hydrophilic monomers (e.g., ethylene oxide) to hydrophobic monomers (e.g., propylene oxide) of from about 90:10 to about 10:90, more preferably, from about 80:20 to about 30:70.
Monomers that may be used to make poly(alkylene oxide) copolymers include ethylene oxide and related glycols as a hydrophilic component and propylene oxide, butylene oxide, trimethylene oxide, tetramethylene oxide and the like and related glycols as a hydrophobic component. The poly(alkylene oxide) copolymers may be terminated with lower alkyl groups, amino groups, hydroxyl groups, carboxylic acid groups, aromatic groups, or other nonreactive groups.
Examples of useful poly(alkylene oxide) copolymers include, but are not limited to, those poly(alkylene oxide) copolymers available under the trade designations TETRONIC(trademark) (tetrafunctional block copolymers derived from sequential addition of propylene oxide and ethylene oxide to ethylene diamine with hydrophilic endblocks) and TETRONIC(trademark) R (tetrafunctional block copolymers derived from sequential addition of propylene oxide and ethylene oxide to ethylene diamine with hydrophobic endblocks) copolymers available from BASF, Mt. Olive, N.J.; PLURONIC(trademark) (triblock copolymers with poly(ethylene oxide) end blocks and poly(propylene oxide) midblock) and PLURONIC(trademark) R (triblock copolymers with poly(propylene oxide) endblocks and poly(ethylene oxide) midblock) copolymers available from BASF; UCON(trademark) Fluids (random copolymers of ethylene oxide and propylene oxide) available from Union Carbide, Danbury, Conn.; and JEFFAMINE(trademark) poly(alkylene oxide) copolymers available from Huntsman Chemical Corporation, Houston, Tex. Various combinations of poly(alkylene oxide) copolymers can be used in the wet-stick adhesives of the present invention.
Preferably, the poly(alkylene oxide) copolymer can be used in an amount of at least about 9 weight percent (wt-%), based on the total weight of the adhesive composition (e.g., the copolymerized (meth)acrylate/hydrophilic acidic comonomers and poly(alkylene oxide) copolymer). More preferably, the poly(alkylene oxide) copolymer is used in an amount of at least about 13 wt-%, and most preferably, at least about 20 wt-%. Preferably, the poly(alkylene oxide) copolymer can be used in an amount of no greater than about 30 wt-%. The amount of poly(alkylene oxide) copolymer required depends upon the type and ratios of the (meth)acrylate and hydrophilic acidic comonomers employed in the polymerizable mixture and the type and molecular weight of the poly(alkylene oxide) copolymer used in the adhesive composition.
Crosslinkers
In order to improve shear or cohesive strength, control elastic modulus and preadhesion tack, for example, of the adhesives of the present invention, the copolymers present in the adhesive can be crosslinked. Preferably, the crosslinking agent is one that is copolymerized with the reactive monomers. The crosslinking agent may produce chemical crosslinks (e.g., covalent bonds). Alternatively, it may produce physical crosslinks that result, for example, from the formation of reinforcing domains due to phase separation or acid base interactions. Suitable crosslinking agents are disclosed in U.S. Pat. No. 4,379,201 (Heilman), U.S. Pat. No. 4,737,559 (Kellen), U.S. Pat. No. 5,506,279 (Babu et al.), and U.S. Pat. No. 4,554,324 (Husman). Combinations of various crosslinking agents can be used to make the copolymers present in the adhesives of the present invention. It should be understood, however, that such crosslinking agents are optional.
Suitable crosslinking agents include thermal crosslinking agents such as a multifunctional aziridine, for example. Other crosslinkers include 1,6-hexanedioldiacrylate and trimethylolpropane triacrylate, and substituted triazines, and the chromophore-substituted halo-s-triazines described in U.S. Pat. No. 4,329,384 (Vesley) and U.S. Pat. No. 4,330,590 (Vesley).
Another class of suitable agents are the copolymerizable monoethylenically unsaturated aromatic ketone monomers free of ortho-aromatic hydroxyl groups such as those disclosed in U.S. Pat. No. 4,737,559 (Kellen). Yet another class of suitable crosslinking agents are the multifunctional radiation-activatable crosslinking agents described in International Publication No. WO 97/07161 (assigned to 3M Company), and in U.S. Pat. No. 5,407,971 (Everaerts et al.). Also suitable are hydrogen-abstracting carbonyls such as anthraquinone, benzophenone, and derivatives thereof, as disclosed in U.S. Pat. No. 4,181,752 (Martens et al.).
Other suitable crosslinking agents include chemical crosslinkers that rely upon free radicals to carry out the crosslinking reaction. Reagents such as peroxides, for example, serve as a precursor of free radicals. When heated sufficiently, these precursors will generate free radicals that bring about a crosslinking reaction of the polymer chains.
Aside from thermal or photosensitive crosslinkers, crosslinking may also be achieved using high energy electromagnetic radiation such as gamma or e-beam radiation, for example.
A physical crosslinking agent may also be used. In one embodiment, the physical crosslinking agent is a high Tg macromer such as those that include vinyl functionality and are based upon polystyrene and polymethylmethacrylate. Such vinyl-terminated polymeric crosslinking monomers are sometimes referred to as macromolecular monomers (i.e., xe2x80x9cmacromersxe2x80x9d). Such monomers are known and may be prepared by the methods disclosed in U.S. Pat. No. 3,786,116 (Milkovich et al.) and U.S. Pat. No. 3,842,059 (Milkovich et al.), as well as Y. Yamashita et al., Polymer Journal, 14, 255-260 (1982), and K. Ito et al., Macromolecules, 13, 216-221 (1980).
If used, the crosslinking agent is used in an effective amount, by which is meant an amount that is sufficient to cause crosslinking of the pressure-sensitive adhesive to provide adequate cohesive strength to produce the desired final adhesion properties to the substrate of interest. Preferably, if used, the crosslinking agent is used in an amount of about 0.1 part to about 10 parts, based on 100 parts of monomers.
Other Additives
Other additives can be included in the polymerizable mixture or added at the time of compounding or coating to change the properties of the adhesive. Such additives, or fillers, include pigments, glass or polymeric bubbles or beads (which may be expanded or unexpanded), fibers, reinforcing agents, hydrophobic or hydrophilic silica, toughening agents, fire retardants, antioxidants, finely ground polymeric particles such as polyester, nylon, and polypropylene, and stabilizers. The additives are added in amounts sufficient to obtain the desired end-use properties.
Polymerization Initiators
A free radical initiator is preferably added to aid in the copolymerization of (meth)acrylate and acidic comonomers. The type of initiator used depends on the polymerization process. Photoinitiators which are useful for polymerizing the polymerizable mixture of monomers include benzoin ethers such as benzoin methyl ether or benzoin isopropyl ether, substituted benzoin ethers such as 2-methyl-2-hydroxypropiophenone, aromatic sulfonyl chlorides such as 2-naphthalenesulfonyl chloride, and photoactive oxides such as 1-phenyl-1,1-propanedione-2-(O-ethoxycarbonyl)oxime. An example of a commercially available photoinitiator is IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethane-1-one, commercially available from Ciba-Geigy Corporation). Examples of suitable thermal initiators include AIBN (2,2xe2x80x2-azobis(isobutyronitrile), hydroperoxides, such as tert-butyl hydroperoxide, and peroxides, such as benzoyl peroxide, cyclohexane peroxide, and the VAZO 52, VAZO 64, VAZO 67, and VAZO 88 initiators, which are substituted azonitrile compounds, commercially available from Dupont Company. Generally, the initiator is present in an amount of about 0.005 part to about 1 part based on 100 parts of total monomer.
Polymerization Chain Transfer Agents
Optionally, the composition also includes a chain transfer agent to control the molecular weight of the polymerized compositions. Chain transfer agents are materials that regulate free radical polymerization and are generally known in the art. Suitable chain transfer agents include halogenated hydrocarbons such as carbon tetrabromide; sulfur compounds such as lauryl mercaptan, butyl mercaptan, ethanethiol, isooctylthioglycolate (IOTG), 2-ethylhexyl thioglycolate, 2-ethylhexyl mercaptopropionate, 2-mercaptoimidazole, 2-mercaptoethyl ether, and alcohols (e.g., isopropanol), and mixtures thereof. The amount of chain transfer agent that is useful depends upon the desired molecular weight and the type of chain transfer agent. The chain transfer agent is typically used in amounts from about 0.001 part to about 10 parts by weight per 100 parts of total monomer.
Methods of Making Adhesive Compositions
The wet-stick pressure-sensitive adhesives of the present invention can be prepared by a wide variety of conventional free radical polymerization methods as described in textbooks and open literature such as xe2x80x9cPrinciples of Polymerizationxe2x80x9d by George Odian, published by McGraw-Hill Book Company. Specific polymerization methods used in this invention are discussed under xe2x80x9cGENERAL PROCEDURESxe2x80x9d in the Examples.
In one solution polymerization method, the alkyl (meth)acrylate monomers and acidic monomers, and poly(alkylene oxides), along with a suitable inert organic solvent, and free radically copolymerizable crosslinker, if used, are charged into a four-neck reaction vessel which is equipped with a stirrer, a thermometer, a condenser, an addition funnel, and a temperature controller. After this monomer and poly(alkylene oxide) copolymer mixture is charged into the reaction vessel, a concentrated thermal free radical initiator solution is added to the addition funnel. The whole reaction vessel and addition funnel and their contents are then purged with nitrogen to create an inert atmosphere. Once purged, the solution within the vessel is heated to decompose the added thermal initiator, and the mixture is stirred during the course of the reaction. A conversion of about 98 percent to about 99 percent is typically obtained in about 20 hours. If desired, solvent can be removed to yield a hot melt coatable adhesive. Suitable inert organic solvents, if required, may be any organic liquid which is inert to the reactants and product and will not otherwise adversely affect the reaction. Such solvents include ethyl acetate, acetone, methyl ethyl ketones, and mixtures thereof. The amount of solvent is generally about 30 percent by weight to about 80 percent by weight based on the total weight of the reactants (monomer, poly(alkylene oxide) crosslinker, initiator) and solvent.
Another polymerization method is the ultraviolet (UV) radiation initiated photopolymerization of the monomer mixture. This composition, along with suitable photoinitiator, crosslinker and poly(alkylene oxide) copolymer, is coated onto a flexible carrier web and polymerized in an inert, i.e., oxygen-free, atmosphere, such as a nitrogen atmosphere, for example. A sufficiently inert atmosphere can be achieved by covering a layer of the photoactive coating with a plastic film that is substantially transparent to ultraviolet radiation, and irradiating through that film in air using fluorescent-type ultraviolet lamps that generally give a total radiation dose of about 500 milliJoules/cm2.
Solventless polymerization methods, such as exposure to ultraviolet (UV) radiation as described in U.S. Pat. No. 4,181,752 (Martens), the continuous free radical polymerization in an extruder described in U.S. Pat. No. 4,619,979 (Kotnour, et al.) and U.S. Pat. No. 4,843,134 (Kotnour, et al.); the essentially adiabatic polymerization methods using a batch reactor described in U.S. Pat. No. 5,637,646 (Ellis); and, the methods described for polymerizing packaged pre-adhesive compositions described in U.S. Pat. No. 5,804,610 (Hamer, et al.) may also be utilized to prepare the polymers. In using such methods, the package would include the reactive monomers and the nonreactive poly(alkylene oxide) copolymer.
The adhesive compositions of the present invention may be applied to a backing by a variety of coating methods, including brush, roll, spray, spread, wire, gravure, transfer roll, air knife, or doctor blade coating.
If the composition includes an organic solvent or water, it is then dried at a temperature (e.g., about 65xc2x0 C. to about 120xc2x0 C.) and a time (e.g., several minutes to about one hour) so as to provide an adhesive tape or dressing, for example. The thickness of the layer of adhesive may vary over a broad range of about 10 microns to several hundred microns (e.g., about 200 microns).
Once the adhesive composition has been coated, and optionally crosslinked, the adhesive surface of the article may, optionally, be protected with a temporary, removable release liner (i.e., protective liner) such as a polyolefin (e.g., polyethylene or polypropylene) or polyester (e.g., polyethylene terephthalate) film, or a plastic film. Such films may be treated with a release material such as silicones, waxes, fluorocarbons, and the like.
Backings and Articles
The wet-stick pressure-sensitive adhesives of the present invention that adhere to wet or moist skin and similar surfaces are useful in many medical applications. For example, these wet-stick adhesives are useful in medical applications such as tapes, bandages, dressings, and drapes to adhere to moist skin surfaces such as wounds or areas of the body prone to moistness.
The adhesive compositions can be included in a variety of dressing constructions known in the art. Typically, the composition is in the form of a continuous or discontinuous coating on at least one major surface of a backing. The backing may include one or more layers and be in a variety of forms (e.g., foams or films). Examples of suitable backings include materials with a relatively low content of hydrophilic components such as polyester (e.g., commercially available under the designation HYTREL(trademark), such as HYTREL 4056, from DuPont Co.), polyurethane (e.g., commercially available under the designation ESTANE(trademark), such as ESTANE 58309 and ESTANE 58237, from B.F. Goodrich Co.), polyether block amide (e.g., commercially available under the designation PEBAX(trademark), such as PEBAX 2533 and 3533, from Atochem Co.), and porous polyethylene resins. Also suitable are materials having relatively high moisture vapor transmission properties. Examples include certain polyether amides such as PEBAX 4011RN00 (Atochem Co.), and polyurethanes as described in U.S. Pat. No. 4,598,004 (Heinecke). Both classes of materials may also be used in combination with each other (e.g., in sandwich-type arrangements) to tailor the moisture vapor transmission properties of the dressing. Examples of specific dressing configurations for which the compositions are suitable are described in U.S. Pat. No. 4,952,618 (Olsen).